|From:||R Andrew Hayden <rahayden@*****.WEEG.UIOWA.EDU>|
|Date:||Sat, 30 Jan 93 22:12:37 CET|
(c) 1990 Grolier Electronic Publishing, Inc.
The automobile is a self-propelled, four-wheeled, steerable vehicle
for transporting people on land. This article describes the main parts of
the automobile and their components. The history, manufacture, and design
of the motorized passenger vehicle are discussed in AUTOMOTIVE INDUSTRY.
Technical and operational details are to be found in separate articles on
the systems mentioned below.
All passenger cars, trucks, and buses have certain things in common:
(1) the power plant, or ENGINE; (2) the chassis, which supports the
engine and wheels and includes the frame and the steering and brake
systems; (3) the power train, which transmits the power from the engine
to the car wheels; and (4) the body.
A variety of engine types have been used in foreign and domestic
vehicles. They are generally INTERNAL-COMBUSTION ENGINES that burn
gasoline or diesel fuel oil. Internal-combustion engines can be classified
in several ways. Of the many possibilities, most passenger-car engines run
on gasoline, have spark ignition, and are of the liquid-cooled,
four-stroke-cycle, overhead-valve, carbureted, reciprocating type.
DIESEL ENGINES, which burn fuel oil, are becoming more common in
automobiles. Diesel engines inject fuel into the cylinders, where it is
ignited by the heat of compression; they do not require spark IGNITION
Most engines have carbureted fuel systems; these mix gasoline with
air in the CARBURETOR to form a combustible mixture. All diesel engines
and some gasoline engines, however, use fuel injection instead of a
carburetor. In the diesel engine, the fuel is injected directly into the
Almost all automobiles use reciprocating engines, which have pistons
that move up and down in cylinders. The crankshaft, the main shaft of the
engine, converts the reciprocating motion of the pistons into rotary
motion. Some, however, use WANKEL ENGINES, which are a rotary type of
The chassis includes the car frame, power train, wheels, suspension,
and steering and brake systems.
Two types of frames, full and stub, are used. The full frame has
side, front, back, and cross members welded into a single assembly that
supports all other parts of the vehicle. The stub frame has separate
frames for the front and back that are welded to the car body, with the
body forming the center and connecting support.
The wheels are attached to the frame by any of three types of
springs: coil, leaf, and torsion bar. All SUSPENSION SYSTEMS use shock
absorbers, which control the up-and-down movement of the wheels and
prevent excessive wheel movement.
The STEERING SYSTEM normally controls the turning of the front
wheels. As the steering wheel is turned, a gear under the hood changes
the rotary motion into side-to-side motion, which is then transmitted to
steering arms on the wheel supports and causes the wheels to turn. On
many cars, power from the engine eases the effort of turning the steering
In the BRAKE system, a brake fluid in the master cylinder is forced
through brake lines to wheel mechanisms when the driver depresses the
brake pedal. The pressure of the fluid forces brake shoes or pads to
press against drums or disks that are attached to the moving wheels.
Friction causes the wheels to slow or stop. with power brakes, power
fromt he engine is used to increase the pressure activating the piston in
the master cylinder.
Among several impressive new developments are mechanisms that allow
all four wheels--rather than simply the two front wheels--to steer the
car, permitting easier parking and greater stability at highway speeds;
and antilock brakes that prevent skidding, even under wet or icy
The power train includes a TRANSMISSION, manual or automatic; a
clutch, on cars with manual transmission; a drive shaft; a DIFFERENTIAL;
and wheel axles. Although most conventional American cars use a
front-mounted engine to drive the rear wheels, an increasing number of
newer models use front-wheel drive, where the weight of the engine on the
front wheels provides better traction on slippery roads. In some cars
designed particularly for bad weather and rough roads, the engine drives
all four wheels.
Open cars (convertibles) are recovering their popularity, after a
period when they were not made because of the dangers of rooflessness in
The purpose of the transmission is to permit a change in the gear
ratio between the engine crankshaft and the driven wheels. When the
vehicle is started from rest, the ratio must be high so that the engine
can turn at higher speeds and develop enough power to accelerate the car.
As the vehicle speed increases, the transmission is shifted upward once or
several times to decrease the gear ratio. The shift is accomplished in
manual transmissions by a shift lever operated by the driver. The
automatic transmission makes the shifts without driver intervention.
On cars with manual transmissions, a clutch, a device for connecting
and disengaging the engine, is used to relieve the driving pressures
through the transmission as gears are shifted. Internal clutches in the
automatic transmission perform this function automatically.
The drive shaft, or propeller shaft, connects the transmission with
the differential, an arrangement of gears that allows the wheels to rotate
at different rates when a car is turning. The drive shaft contains two
types of joints: a slip joint and one or more universal joints. This
allows the shaft to change its length and direction as the car wheels move
up and down. In rear-drive cars with engines at the front, one drive
shaft is needed. In front-drive cars with front-mounted engines, two are
needed, one to each front wheel.
William H. Crouse
Appel, Robert, The Car Owner's Survival Guide (1986); Crouse, William H.,
and Anglin, Donald L., The Auto Book, 3d ed. (1983); Day, John, The Bosch
Book of the Motor Car: Its Evolution and Engineering Development (1976);
Ellinger, Herbert E., Automechanics, 2d ed. (1977); Masterman, Eric V.,
The Auto Compendium (1986); Sears, Stephen W., The American Heritage
History of the Automobile in America (1977); Whipp, Richard, and Clark,
Peter, Innovation and the Automotive Industry (1986).
See also: AUTOMOTIVE INSTRUMENTATION; EXHAUST SYSTEM; SAFETY,
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